1. Field of the Invention
The present invention relates to devices for undersea mining, and in particular to devices adapted for the extraction and upward conveyance from the bottom of a body of water of such deposits as ore nodules, mineral soaps, and ore sludge.
2. Description of the Prior Art
In cases where deposits are to be extracted from shallow water depths, the most commonly used extraction devices, besides suction dredges, are such mechanical devices as scoop dredges, grab bucket dredges, and bucket chain dredges, the extracting operation being performed in almost all cases without the use of a separate receiving unit placed on the bottom of the water course. Chain dredges have an advantage under these conditions, becuase they are simple in construction and easy to supervise, while the materials are conveyed upwardly in a continuous operation and extracted in a uniform manner along a predetermined path of advance. This type of prior art device normally has an endless bucket chain moving around a chain drum mounted at the far end of a swivel arm. The two chain strands move on the upper and lower side of the swivel arm, so as not to interfere with each other.
In the case of mining operations in greater water depths, preference has been given in the past primarily to the hydraulic conveyance of the materials, the latter being fed to the conveying unit from a receiving unit which moves along the ocean floor. One shortcoming of these devices is that they are too complex and therefore subject to frequent breakdown, in addition to the fact that they are comparatively inefficient.
Another type of prior art device employs as a conveying device a cable loop running between cable pulleys, one pulley being arranged on board a ship or on board some other suitable carrier floating on the surface, the other pulley being mounted on a mobile receiving unit on the ocean floor. Such a conveyor may use two conveying baskets moving in a shuttle-type operation, an arrangement which is suitable only for relatively shallow water depths, or it may have a series of buoyant carriers which move in a rotating operation. However, both the design and the necessary controls for this type of buoyant carrier are comparatively complex, so that they, too, are subject to frequent operational problems, in addition to the relatively low conveying capacity of the buoyant carriers. Lastly, the conveying cables lack any positive guide between the reversal points at the cable pulleys, making it possible for the conveying baskets to collide with each other in mid-course.
In order to avoid the last-mentioned problem, it has already been suggested to use a cable loop system with a series of pivotably attached carrying baskets in which the cable loop runs downwardly from the bow of the ship and returns at the stern of the ship, over appropriate cable guide means, a large length portion of the cable loop being dragged along the ocean floor, as a result of the lateral drift of the ship (U.S. Pat. No. 3,672,079). This system, however, is subject to the risk that even small obstacles encountered on the ocean floor may cause the conveying cable to become hooked, resulting in possible damage or even rupture of the cable.